MP2316 Rev. 1.11

www.MonolithicPower.com

12

4/11/2017

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OPERATION

PWM Operation

The MP2316 is a fully-integrated, synchronous,

rectified, step-down switch converter. The device

uses constant-on-time (COT) control to provide

fast

transient

response

and

easy

loop

compensation. Figure 2 shows the simplified

ramp compensation block in MP2316, at the

beginning of each cycle, the high-side MOSFET

(HS-FET) turns ON whenever the ramp voltage

voltage

indicates

insufficient

output voltage. The input voltage and the

frequency-set resistor determine the high-side

After the ON period elapses, the HS-FET enters

the OFF state. By cycling HS-FET between the

ON and OFF states, the converter regulates the

output voltage. The integrated low-side MOSFET

(LS-FET) turns on when the HS-FET is in its OFF

state to minimize the conduction loss.

Shoot-through occurs when there is both HS-FET

and LS-FET are turned on at the same time,

causing a dead short between input and GND.

Shoot-through dramatically reduces efficiency,

and the MP2316 avoids this by internally

generating a dead-time (DT) between HS-FET is

off and LS-FET is on, LS-FET is off and HS-FET

is on. The device enters either heavy-load

operation or light-load operation depending on

the output current.

Figure 2—Simplified Ramp Compensation

Block

MODE Selection

As shown in Figure 3, connecting a resistor (R6)

from FREQ/MODE pin to VIN can set the

switching frequency and meanwhile, the part will

work at forced PWM mode. Connect a resistor

(R7) from FREQ/MODE pin to GND can set the

switching frequency and meanwhile the part

works at auto PFM/PWM mode.

Figure 3—Mode Selection

Switching Frequency

MP2316 uses constant-on-time (COT) control

and there is no dedicated oscillator in the IC. The

input voltage is feed-forwarded to the on-time

one-shot timer through the frequency resistor, the

frequency is fairly constant over the input voltage

range.

The

approximate

typical

switching

frequency can be determined with the following

equation:

6

SW

IN

on

OUT

10

F(KHz)

V(V)

T(ns)

V(V)





(1)

and Auto PFM/PWM mode.

The approximate

typical Ton formula is shown below:

Forced PWM mode:

FREQ

ON _ PWM

DELAY _ PWM

IN

14.5 R

(k )

TT

(ns)

V(V) 0.4









(2)

Auto PFM/PWM mode,

FREQ

ON _ PFM

DELAY _ PFM

IN

13 R

(k )

TT

(ns)

V(V) 0.4









(3)

comparator delay, and the typical value equals

approximately 15ns and 10ns respectively

When part enters CCM mode, the duty ratio will

change slightly from light load to full load due to

power loss. So the frequency will change a little

from light load to full load even in CCM mode.

Because of the minimum on time and minimum

off time, switching frequency is limited. The